Obviously, a premptive US military attack is the last resort. In the meantime, we should work on regime change in Iran, overtly and covertly. We should be aiding the opposition forces inside and outside of Iran. There are various diplomatic levers and economic sanctions that can be employed to further isolate Iran and its efforts to acquire nuclear weapons.
Domestically, Iran's economy is in poor shape and the brain drain is real with more than 150,000 educated young people leave Iran annually for countries such as the U.S. and Canada. Some 4 million Iranians now live abroad. The current regime is very unpopular. The question is can we change it without using military force. We should try given our long term strategic interests in the region and our relationship with our once and future ally, Iran.